Electrically conductive touch pen

ABSTRACT

A combination writing pen and stylus is disclosed. The device has an internal ink cartridge deployable through a hole in the stylus tip. The stylus tip extends from a sleeve that is formed of a conductive elastomeric material. The sleeve extends up a rigid shaft of the device such that it contacts a sufficient ground. The stylus tip may be coated with a protective material that adjusts the coefficient of friction and prevents carbon deposits on the touch screen. A sufficient contact patch is achieved to simulate a human finger so as to overcome false positives from common touch screen logic. This is done by altering tip geometries around an air cavity within the sleeve.

CROSS-REFERENCE TO RELATED APPLICATION

This is a non-provisional patent application claiming priority to U.S.Provisional Patent Application No. 61/476,309, filed on Apr. 17, 2011,entitled “ELECTRICALLY CONDUCTIVE TOUCH PEN.” The provisionalapplication is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to marking utensils and computer inputdevices. More specifically, the invention is directed at multi-functionwriting devices that can physically mark on traditional writing surfacesand can also digitally mark on, or be used as other input means inassociation with, computerized digital displays.

BACKGROUND OF THE INVENTION

Historically, a stylus is an elongated, sharp, pointed instrument usedfor writing, marking, and engraving. More recently styli are beingmodified for use with inputting data to computer devices.

In the context of touch screen computer interfaces, a stylus providesmany benefits to users. For example, a user can more accurately use astylus for computer touch screen input than they can their own finger.The accuracy is due to the fact that a computer stylus has a smaller tipthan do most human fingers, and so can achieve an accordingly higherdegree of accuracy on a touch screen. This increase in accuracy, inturn, allows for smaller user interface elements, and provides increasedease of use for many users. Additionally, some users prefer to use astylus simply to avoid depositing the natural oils from their hands onthe screen.

One disadvantage to stylus use is that it necessitates carrying anadditional personal item. This is especially problematic given thealready large number of personal items commonly carried by individualssuch as: keys, pens, glasses, wallet, and a smart phone. One solution tothis problem is the combination pen and stylus.

A touch screen is, generally speaking, a combination touchpad andcomputer display that can detect the presence and location of a touchwithin the display area. Although this patent application will refergenerally to touch screens, much of the technology disclosed herein willwork with other similar human machine interfaces, such as a touchpad.There are many touch screen technologies including resistive,capacitive, surface acoustic wave, infrared, strain gauge, opticalimaging, dispersive signal technology, inductive sensor systems that maybe placed under an LCD, and acoustic pulse recognition. Of these, thefirst two (resistive and capacitive) are the most common.

Resistive touch screens have been used on smart phones and tabletcomputers. An example of a resistive touch screen is the PALM PILOT®.Resistive touch screens comprise two very slightly separated opticallytransparent sheets, at least one flexible, and both coated with atransparent electrically conductive material. Normally, there is nocontact between the two sheets, however, when the surface of the touchscreen is touched at a point by a stylus or other object, the two sheetscontact each other at that point, registering to the related computersystem the precise location of the touch. This type of touch screen cansense contact from nearly any solid object pressed against it.Accordingly, nearly any pointed object can serve as a stylus.Combination pen/stylus devices already exist for resistive touchscreens. For example, the Dr. Grip 1+1 Stylus Pen Combo manufactured byPILOT® is a combination ballpoint pen and stylus for use with resistivetouch screens. The tips of such devices are typically plastic or asimilar polymer, so as not to damage or scratch the screen.

Capacitive touch screens are quickly replacing resistive touch screens,and are used with many modern small digital devices. For example, thenewer iPhones® and iPads® from APPLE® are all equipped with capacitivetouch screens. Capacitive touch screens generally comprise a flatinsulative transparent sheet such as glass having an inside portioncoated with a transparent conductor such as indium tin oxide (ITO),films made from graphene (carbon nanotubes), or other suitable material.Conductive materials that touch or are in very close proximity to thistype of touch screen alter the electrostatic field of the screen,thereby creating a registerable change in capacitance. At the physicallevel a changing electrical potential difference causes a flow ofelectrons as an alternating current (AC) through a capacitor and it isthis current flowing to a sink or source of electrons that is detectedby the touch screen device. For some conductive materials such asbiological tissue, these charged carriers could be predominantlyions—cations and/or anions. This sink or source of electrons, sometimescalled a “ground” is necessary to complete the flow of electrons in mosttypes of capacitive touch screens that can be activated by human touch.The effectiveness of a body as a ground is directly proportional to theproduct of its volume and conductivity. For alternating current andcomplex materials such as biological tissue it is also dependent on thefrequency of the alternating current.

The most common input device used with capacitive touch screens is thehuman finger. Although the conductivity of the human body is notparticularly high, its relatively high volume nevertheless allows it toact as an effective ground. At low frequencies typical biologicaltissues have conductivities on the order of 1 to 10 S/m (Siemens permeter) compared to metals like copper and aluminum which are 58 and 35MS/m (million Siemens per meter) respectively. Traditional plastic orpolymer-based styli are not effective in marking on capacitive touchscreens because they are not sufficiently conductive. The problem isexacerbated if the user of the stylus is wearing gloves or has extremelydry skin. This is common in colder environments, where people may oftenneed to mark on handheld devices while outside. These situations areproblematic because the user is further insulated from the stylus whichprevents the flow of alternating current to the human body ground.Though other materials providing better conductivity could be used, suchas aluminum or other metals, they would likely scratch or otherwisedamage the touch screen. Furthermore, many capacitive touch screens aretuned to detect inputs from human fingers and thus may not register ahard pointed input, simply due to the goal of minimizing false inputs.

One solution that enables a stylus to be used with a capacitive touchscreen is the use of conductive rubber or a similar conductiveelastomeric material. Conductive rubber is a rarer and more expensiveform of rubber that contains suspended graphite carbon, carbonnanotubes, nickel or silver particles. Its electrical impedancedecreases when it is compressed, and the capacitance increase as aresult of the larger surface area in contact with the touch screen,thereby making it useful for capacitive touch screen applications. Inaddition, the rubber durometer can be set so as to deform at its tip ina manner similar to the deformation exhibited by a human finger as itpresses down on a flat surface.

What is missing in the present art is a writing device that canseamlessly transition between marking on paper and marking on acapacitive screen. Such combinations for resistive-screen styli like thePILOT® pen proved easy because a rigid, non-conductive end of a pencould be used. For capacitive screens, no such device exists in theprior art because of the challenges with mounting a writing pen within asufficiently flexible, sufficiently conductive material.

SUMMARY OF THE INVENTION

The invention described herein may be operated as either a pen forwriting on paper or other surfaces, or as a stylus for interacting witha capacitive touchpad or touch screen. The device is easy to use, andconversion between the two modes is accomplished by any standardretractable pen-type interface, such as a push button or twistingmovement. An embodiment of the device works even if the user iseffectively insulated from the electrically conductive stylus pen, e.g.,if the user is wearing gloves. The device comprises electricallyconductive rubber with a proper screen-protective coating, and featuresa compliant tip which generates the proper contact area when the stylusis depressed against a touch screen.

According to certain embodiments, the invention provides an electricallyconductive touch pen that has a conductive, flexible tip. The inventionattempts to model the contact area of a human finger with the flexibletip to improve conductivity and simulate the touch of a human fingertip.It is this contact area that determines the electrical impedance (i.e.capacitance in this case), because the substrate of the touch screen isusually a very good insulator (e.g., glass). Because capacitance isdirectly proportional to the common area of the conducting surfaces ofthe touch screen on the one hand and the conductive rubber on the other,a large contact patch is desirable.

It is an object of the present invention to provide an electricallyconductive touch pen which may be employed by a user with very dry skinor who is wearing gloves, e.g. a user who does not make conductivecontact with the combination pen and stylus.

It is an additional object of the invention to provide a stylus rubbertip in electrical contact with a good conductor such as, but not limitedto, copper or aluminum of such mass that the product of its electricalconductivity and volume, at the frequency of operation, is functionallyequivalent to that of the human body.

It is an additional object of the invention to provide a pen/styluscombination, wherein the pen deploys and retracts from within a housingcreated by the stylus material, and wherein the housing comprises asufficient air cavity to promote a proper contact area with the touchscreen when the pen is retracted.

It is an additional object of the invention to provide a plurality ofremovable styli caps for a writing device that can be placed over thewriting device, the plurality of caps having an adjustable range of endtip pliability so as to adjust the conductivity and contact patch fordifferent environmental conditions and touch screen devicecharacteristics.

While certain features and embodiments are referenced above, these andother features and embodiments of the present invention will be, or willbecome, apparent to one having ordinary skill in the art uponexamination of the following figures and detailed description. It isintended that all such additional embodiments and features includedwithin this description, be within the scope of the present invention,and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE FIGURES

The present invention can be better understood with reference to thefollowing drawings. The components in the drawings are not necessarilyto scale, emphasis instead being placed upon clearly illustrating theprinciples of the present invention. In the drawings, like referencenumerals designate corresponding parts throughout the several views.

FIG. 1 is an environmental view of the electrically conductive touch penwith the writing tip retracted and the stylus in operation on a touchscreen in accordance with a certain embodiment.

FIG. 1A is an environmental view of the electrically conductive touchpen with a writing tip deployed in accordance with a certain embodiment.

FIG. 2 is a perspective view of the electrically conducive touch pen ina first configuration according to a certain embodiment of theinvention.

FIG. 3 is a perspective view of the electrically conducive touch pen ina second configuration according to a certain embodiment of theinvention.

FIG. 4 is a side view of the electrically conductive touch pen in theconfiguration of FIG. 3.

FIG. 5 is the same view of FIG. 4, but after the stylus tip has engageda touch screen surface.

FIG. 6 is a cross sectional view taken along cutline A-A of FIG. 4, withadditional cross sections 7-7 and 8-8 shown.

FIG. 7 is a cross sectional view taken along cutline B-B of FIG. 6.

FIG. 8 is a cross sectional view taken along cutline C-C of FIG. 6.

FIG. 9 is a cross sectional view similar to FIG. 7, but representing analternative embodiment of the invention.

FIG. 10 is a perspective view representing an alternative embodiment ofthe invention.

FIGS. 11-13 are side views of an alternative embodiment of the inventionwith certain parts removed or partially removed to focus on thedifferent extension lengths.

FIGS. 14 and 15 are side views of the embodiment of FIGS. 11-13, butwith the pen tip included in first and second positions.

FIG. 16 is an isometric view of the touch pen according to a particularembodiment.

FIG. 17 is an exploded view of the components of the touch pen shown inFIG. 16.

FIGS. 18, 19, 20, and 21 are sectioned side views of the writing end oftouch pens having modified tip geometries according to particularembodiments.

FIGS. 18A, 19A, 20A and 21A are sectioned perspective views of theinside of conductive rubber sleeves having modified tip geometriesaccording to particular embodiments.

FIG. 22 is a section view of another embodiment of the touch pen,wherein a separate ring is used as a connection piece.

FIG. 22A is an exploded view of the touch pen of FIG. 22, wherein thering has been removed.

DETAILED DESCRIPTION

The description that follows describes, illustrates and exemplifies oneor more particular embodiments of the present invention in accordancewith its principles. This description is not provided to limit theinvention to the embodiments described herein, but rather to explain andteach the principles of the invention in such a way to enable one ofordinary skill in the art to understand these principles and, with thatunderstanding, be able to apply them to practice not only theembodiments described herein, but also other embodiments that may cometo mind in accordance with these principles. The scope of the presentinvention is intended to cover all such embodiments that may fall withinthe scope of the appended claims, either literally or under the doctrineof equivalents.

It should be noted that in the description and drawings, like orsubstantially similar elements may be labeled with the same referencenumerals. However, sometimes these elements may be labeled withdiffering numbers, such as, for example, in cases where such labelingfacilitates a more clear description. Additionally, the drawings setforth herein are not necessarily drawn to scale, and in some instancesproportions may have been exaggerated to more clearly depict certainfeatures. Such labeling and drawing practices do not necessarilyimplicate an underlying substantive purpose. As stated above, thepresent specification is intended to be taken as a whole and interpretedin accordance with the principles of the present invention as taughtherein and understood to one of ordinary skill in the art.

FIGS. 1 and 1A are environmental views showing a touch pen 10 in usewith a touch screen 3 and a sheet of paper 4, respectively. For purposesof this application, where a touch screen is shown, it will be presumedthat it is a capacitive type touch screen as defined in more detail inthe background section. In FIG. 1, the touch pen, which may also bereferred to herein as an input device or marking device, is in a firstconfiguration where the writing tip 12 is in a stored or retractedposition within the stylus tip 22. In this first configuration, thetouch pen 10 is prepared to mark on or otherwise interact with the touchscreen 3. In FIG. 1A, the writing tip 12 has been deployed to anoperating position where it extends from the stylus tip. In this secondconfiguration, the touch pen 10 is prepared to mark on a traditionalwriting surface such as paper 4.

As shown, the combination touch pen 10 comprises an elongated shaft 14having a writing or marking end (the distal end) and an opposite end(the proximate end). Though not shown, the proximate end may be equippedwith various features such as a mechanism for deploying the writing tip12, a light, an eraser (if the tip 12 is lead-based), etc. The pen alsocomprises a sheath or sleeve 20 that covers and extends beyond thedistal end of the shaft 14. This sleeve 20 is formed of an elasticmaterial with conductive properties that are sufficiently resilient, yetrebound to an original molded shape after moderate deformation.Non-limiting examples of such material are silicone rubber, naturallatex rubber, thermoplastic elastomers (TPE), thermoplastic vulcanizates(TPE-v), thermoplastic urethanes (TPU), and ethylene-vinyl acetates(EVA), each having additives such as carbon, copper, nickel or silverfragments. Different variations of these materials and additives may beused to affect the appearance, color and translucence of the sleeve.Where the term “rubber” is used herein, it will be understood that anyof the above materials could be substituted.

As an alternative to the metal fragments, a metal mesh or otherconfiguration (not shown) could be used as an insert to the mold suchthat the elastomeric compound would be formed around and cover over it.In this case, the mesh would be thin enough to be sufficiently flexibleand may not extend all the way to the end of the style tip 22. In theembodiment shown, the sleeve 20 extends some distance up the shaft 14such that it is gripped by the hand of a user. In this fashion, shaft 14may be formed of any rigid material, whether conductive or not. Forexample, shaft 14 could be an inexpensive, non-conductive plastic orother polymer. This is because touch pen 10 is designed in thisembodiment such that the conductive sleeve 20 directly contacts the userfor a sufficient ground.

FIGS. 2 and 3 show closer views of the distal end of the touch pen 10.In FIG. 2, the writing tip 12 is extended through a central hole 24along the stylus tip 22. In FIG. 3, the writing tip is retracted and thestylus tip 22 is ready to engage a touch screen. The conductive sleeve20 expands in diameter along its out surface from the stylus tip 22until it reaches a necking point 26. The increased diameter from thenecking point 26 rearward is sized to accommodate the shaft 14 and/orother internal components of the touch pen 10, as shown in laterfigures. Further up the sleeve is a shoulder that expands to an evenlarger diameter used across a gripping section 19 of the touch pen. Thegripping section may have contours, as shown, to increase comfort for auser and invite that particular portion of the touch pen 10, which iscovered by the conductive sleeve, to be gripped in hand to form aground.

FIGS. 4 and 5 show the distal end of touch pen 10 in the stylusconfiguration first preparing to, and then engaging, a touch screensurface 3. The stylus tip 22 noticeably deforms when it is pressedagainst the surface of the touch screen 3. Again, this is by design inorder to increase the contact area, and thus the capacitive propertiesof the elastomeric material that forms the stylus tip 22. It alsoincreases the surface area in a manner so as to model the size andfootprint of a human finger as a method to overcome touch screen logicthat may be designed to ignore false (non-finger) inputs.

The stylus material should be soft and highly elastic to achieve thisdesired level of deformation, yet it should have exceedingly goodpositional memory to return to its proper shape in order to correctlyposition the central hole 24 from which the writing tip 12 protrudes.This challenge is exacerbated by the fact that adding the requiredcarbon-based material to the rubber (or other elastic material asdescribed above) to obtain the desired level of conductivity tends tostiffen the compound. To offset this factor, one method is to use softerrubber (i.e., having a lower durometer). For a solid rubber tip, or onewith a narrow internal diameter hole, one needs a very soft rubber. Theuse of such a soft rubber is difficult due to problems with manufacture,structural effect, aesthetics, and durability. Another alternative, asshown in later figures, is to alter the wall thickness of the sleeve 20beyond the necking point 26, thus creating an internal air cavity. Aswill become more clear, the ideal scenario involves a combination ofproper durometer rubber and specific wall thickness variance.

FIG. 6 shows a section view taken along section line A-A shown in FIG.4. The stylus tip of FIG. 6 has a solid rubber tip with no air cavity.As explained above, it would require a very soft elastomeric material inorder to have the flexibility needed to produce the desired surfacecontact. The sleeve 20 of FIG. 6 is comprised of the conductive cover 28and an inner molding 29. In this case, only the conductive cover 28portion of sleeve 20 is formed of the conductive elastic materials asdescribed above. The inner molding 29 need not be conductive, and shouldbe rigid or semi-rigid so as to properly house and provide support forthe ink cartridge 13 that is disposed within it. The conductive cover 28comprises the entire tip portion from the necking point 26 down to thefar end of the stylus tip 22. Though it thins out considerably, theconductive cover 28 also covers the inner molding 29 as the coverextends back up toward the shaft 14 (not shown). Again, this is toensure contact with a ground source.

In the illustrated embodiment, the molding 29 has a hollow inner core27, so as to save unnecessary material costs. The molding 29 connects tothe shaft 14 further up the touch pen 10. The conductive cover 28 may bebonded to the molding 29, or it may simply be stretched or rolled overthe molding 29, adhering thereto by way of an interference fit. Eitherway, the conductive cover 28 and inner molding 29 may typically beremoved from the shaft as one assembly. In other embodiments, themolding 29 may be replaced completely by the shaft 14, which wouldextend further down and be covered directly by the conductive cover 28.

FIGS. 7 and 8 show radial cut-away views along section lines B-B andC-C, respectively. As may be seen, the electrically conductive flexiblematerial is continuous around the outer surface of the touch pen at thesection B point, but does not completely surround the touch pen at thesection C point. The conductive material content at the Section C pointis sufficient to form a steady contact with a user's fingers, and isless costly than completely covering the circumference of the innermolding 29. This arrangement offers the additional advantage ofproviding a textured surface for the user to contact, which improves auser's ability to grip the electrically conductive stylus pen.

FIG. 9 depicts a cut-away view along line B-B of an alternativeembodiment of the touch pen 10. In this alternative embodiment thesingle pen tip of the preferred embodiment has been replaced by aplurality of pen tips 12 a, 12 b, and 12 c, each of which is attached toseparate ink cartridges. This serves to show that the stylus/pencombination of the present design can accommodate numerous variationsand combinations of known writing utensil features and functions. Inthis case, FIG. 9 depicts a touch pen 10 that can write in variouscolors on paper, yet still make marks or selections on a touch screen.

FIGS. 10-15 depict an alternative embodiment of the touch pen 10, wherethe inner molding 29 is replaced by a former 39 that is ideallymetallic. This alternative embodiment is designed to address theaforementioned problems attendant to a user wearing gloves, having verydry skin, or situations in which the user does not make good conductivecontact with the touch pen 10. In such cases the conductive cover 28needs to be in good electrical contact with a volume of metal V (m3) ofconductivity a (Siemens per meter S/m) which is a direct measure of theeffective number of free electrons or other charged carriers per unitvolume, Ne. Ne is directly proportional to a so Nv=V*σ or Ne=k*V*σ wherek is a constant of proportionality. This is obtained empirically byadding metal material so that the stylus tip operates even when held byan extremely good insulator.

As an exemplary embodiment, a pen comprising a copper former 39 a mayhave a minimum size smaller than the minimum size of a pen comprising analuminum former 39 b. Because the ratio of the density of copper to thatof aluminum is much greater than the ratio of their conductivity (a),such a copper former would likely be heavier for the same electron sinkor source effect. In use, the stylus tip 22 is in good electricalcontact with a good conductor such as copper or aluminum of such massthat the product of its electrical conductivity and volume, at thefrequency of operation, is about the same as that of the human body.This provides an adequate ground for the alternating current i.e. anadequate sink or source of electrons for the stylus to be operated withan insulated or gloved hand. Alternatively, the former 39 could be of anon-conductive material such as plastic. However, this would hamper auser's ability to operate the touch pen 10 with gloves.

As may be seen in FIG. 10, the flexible conductive cover 28 extends upthe former so that a user will contact the flexible conductive cover 28.The former 39 provides sufficient free electrons such that theelectrically conductive stylus pen will function with a conductive touchscreen even if the user is wearing non-conductive gloves. The user couldalso make direct contact with the former but it is generally desirablefor the user to have contact with a soft grip surface.

FIGS. 11-13 provide a cut-away view of the alternative embodiment ofFIG. 10. Though not shown, the ink cartridge 13 is housed within acentral hole in the former 39. Unlike the solid rubber tip of FIG. 6,here is shown that the wall thickness of the stylus tip 22 is trimmedaway so as to create an air cavity 32 to increase the flexibility of thestylus tip 22. As explained above, this allows for the conductive cover28 to be of a more ideal durometer, providing more durability and easeof manufacture. The larger the air cavity 32, the more flexible thestylus tip 22 will become. However, too much flexibility can also leadto false positives. As shown, the former 39 comprises an extension 41 ofvarious sizes. The size of this extension directly controls the size ofthe air cavity 32. In some embodiments, this extension may be acontrollable feature of the touch pen 10, such as by twisting theproximate end counterclockwise relative of the former to increase thelength of the extension or clockwise to decrease its length. Because theinherent settings on touch screens may vary as to what surface area orconductivity they require, such a flexible feature would allow a user to“dial-in” the touch pen 10 to work optimally in association with aparticular touch screen.

FIGS. 14 and 15 provide similar views to those of FIGS. 11-13, howeverthey also depict an ink cartridge 13, which extends through the hollowcore of the former 39. The ink cartridge 13 (and its associated writingtip 12) is shown first in the extended (operating) position, and then inthe retracted (storage) position. Notably, retraction of the inkcartridge 13 largely empties out the air cavity 32, allowing for thestylus tip 22 to operate with the desired flexibility.

Like with the touch pen of FIGS. 1-9, the cover portion 28 in FIGS.10-15 may either be bonded to the former 39 such as with an adhesive, orsimply be stretched over the former 39 with an interference fit. In someembodiments, an adhesive may be used to make the fit permanent. In otherembodiments, it may be desirable to allow for removal of the coverportion 28. As explained below, the exterior surface of the coverportion 28 (or at least the stylus tip portion 22 that contacts thetouch screen) may require a different type of external coating.

A problem with rubber containing carbon sufficient for conductivity isthat it may leave black marks on substrates to which it comes intocontact. In the case of touch screens, these black marks may ultimatelyobscure the screen. Additionally, conducting metal suspensions such asnickel and silver suspended in rubber may scratch the touch screen glasssubstrate. These problems can be solved by coating the rubber, orselectively the rubber tip, with a very thin layer of Parylene. Thisconformal coating, with strong adherence even to rubber, can be madevery thin down to 10 to 50 microns. Because the dielectric constant ofParylene is so high and its thickness so small, it has virtually zeroeffect on reducing the capacitance of the contact area from that causedby the thickness of the glass substrate alone. Additionally, theParylene coating has a relatively low coefficient of friction, therebyallowing a coated rubber to gently glide over a glass surface. Incontrast, due to its high coefficient of friction, a “juddering” effectis often experienced when an uncoated rubber tip is moved over a glasssurface. Other coatings may also be supplemented, such as, for example,Flourobond® by Orion Industries.

FIGS. 16-21 depict components of a touch pen 10 that could have eitheran inner molding 29 or a former 39. However, as discussed below, it isthe geometry of the stylus tips 22 that vary. FIG. 16 shows an isometricview of a touch pen 10 having a shaft 14 and a sleeve 20. In this case,the shaft 14 could extend down toward the stylus tip 22 inside thesleeve 20, or the sleeve could comprise an exterior conductive cover 28bonded to an inner non-conductive molding 29. At the end opposite thestylus tip 22 (referred to herein as the proximate end because it iscloser to the user when the touch pen is in use), the pen provides astandard plunger 42 for deploying the writing tip of an ink cartridge(not shown) through the central hole 24 along the end of the sleeve 20.It will be understood that a variety of conventional methods could beused to deploy the writing tip, such as a twisting action of the shaft14 relative to the sleeve 20, etc.

FIG. 17 shows an exploded view of the touch pen embodiment depicted inFIG. 16, and reveals that it has an inner molding 29, which is in thiscase threaded so as to provide a connection to the shaft 14. The shaftmay be a conductive material such as metal, or a non-conductive materialsuch as plastic, because the conductive cover 28 is directly connectedto a user as a ground when the touch pen 10 is held in a traditionalmanner. Also shown is the full ink cartridge 13 with writing tip 12 thatis housed within the sleeve 20 and shaft 14 during operation. At theproximate end of the ink cartridge is the cartridge controller 44, whichcan take any conventional form to locate and facilitate the deploymentand retraction of the ink cartridge 13.

FIG. 18 shows the components of FIG. 17 in an assembled position insideof the sectioned sleeve 20, with the writing tip 12 in a storedposition. In this configuration, touch pen 10 would be ready to mark onor provide input to a capacitive touch screen. As shown, spring 17 iscaptured within a spring housing 18 formed by the inner wall of theinner molding 29 of sleeve 20. Note that the inner molding 29 extendsslightly beyond the necking point 26 where the sleeve begins to tapertoward the stylus tip 22 a. The length of this extension has an effectsimilar to the length of the extension 41 of the former 39 in FIGS.11-13. That is, the further it extends, the smaller the air cavity 32,which is a significant determinant in the flexibility (and the relatedconductivity and ability to simulate a human finger) of the stylus tip22 a.

Another feature that significantly affects the size of the air cavity isthe wall thickness of the conductive cover 28 a between the neckingpoint 26 (or the distal end of the inner molding 29 where an extensionis used) and the distal end of the stylus tip. FIGS. 18 and 18A depict aconductive cover 18 that has a uniformly thin wall across this section.Such a cover provides a high level of flexibility and a large contactpatch without having to compromise the integrity of the design with theuse of an overly soft rubber or other elastomeric compound. However,such a thin wall may be less durable, and various factors such asenvironmental conditions, user preference for the amount offriction/resistance, user preference for input pressure, or particularsof a given touch screen, may drive a desire for a different tipgeometry.

FIGS. 19, 20 and 21 all provide alternative tip geometries by alteringthe wall thickness of the conductive cover 28 along the air cavitysection 33 of the touch pen 10. The air cavity section 33 is defined asthe longitudinal region from the distal end of the stylus tip 22 to thefirst rigid structure in contact with the flexible conductive cover 28,which may be on either side of the necking point 26. As shown in thediagrammed embodiments, this first rigid structure is the inner molding29, but it could be a component of shaft 14 or former 39 that extendsdownward such as extension 41 of FIGS. 11-13 in other embodiments. Byaltering the wall thickness along the air cavity section, the touch pen10 can achieve different conductive properties that will tailor its useto a particular user and a particular touch screen. In embodiments wherethe entire sleeve 20 is removable, the touch pen 10 may come withmultiple sleeves 20, each having different tip geometries such as thoseshown in FIGS. 18 through 21, so as to provide a user with options tofit different scenarios.

Whereas FIGS. 18 and 18A feature a uniformly thin wall thickness acrossthe air cavity section 33, stylus tip 22 b of FIGS. 19 and 19Aessentially fills in as much of the air cavity 32 as possible withoutobstructing the central hole 24. In this case, the conductive cover 28 band stylus tip 22 b will provide a less flexible tip that will likelyrequire a softer rubber. However, this may be preferable to users insome scenarios. For example, a stiffer tip will provide more preciseinputs with some touch screens.

FIGS. 20 and 20A features stylus tip 22 c at the end of conductive cover28 c. Stylus tip 22 c is a hybrid design between that of tip 22 a ofFIG. 18 and tip 22 b of FIG. 19, and will provide an intermediate optionas to flexibility and material properties. Finally, FIGS. 21 and 21 Afeature multiple air cavity slots 32 a, 32 b, and 32 c falling inbetween a plurality of structural ribs 25. Other variations of theconductive sleeve geometry along the air cavity section, such aspositioning small air bubbles within the walls of the stylus tip 22during the molding process, are also envisioned.

As shown in FIGS. 22 and 22A, other embodiments feature a conductivecover 28 portion of the sleeve 20 that is merely the stylus tip 22component, and a separate ring 50 is used to connect the stylus tip 22to the inner molding 29. The ring 50 and the stylus tip 22 feature anoverlapping lip and groove such that the ring snaps over the lip of thestylus tip. The ring 50 and the inner molding 29 feature interlockingthreads 31A and 31B used to adhere the ring 50 and the stylus tip 22 tothe touch pen 10. In this fashion, the stylus tips 22 areinterchangeable by unscrewing the ring 50 from the inner molding 29.Thus, multiple stylus tip variations, such as 22A-22D of FIGS. 18-21,could be changed easily. This embodiment also features a longer shaft 14that fills the void created by the missing portion of the sleeve 20.This shaft may be metallic (then enabling the embodiment to work wellwith gloved hands) or non-conductive material such as plastic. Ifnon-conductive, the ring may be made of metal and elongated so as toprovide contact to the users hand for a ground.

Accordingly, it should now be clear how the touch pen 10 provides anefficient all-in-one marking solution for both traditional writingsurfaces and capacitive touchscreens, and how optimal performance can beachieved through variations in the stylus tip geometries and placementof a rigid extension or inner molding. Although the stylus has beendescribed with respect to a pen, other advantages are apparent in stillother alternative embodiments wherein the stylus is used in combinationwith a smartpen, which in common forms may include a microphone torecord audio, a speaker for playback, a display, and or an internalmemory for capturing handwritten notes, audio, and drawings.

It should be emphasized that the above-described exemplary embodimentsof the present invention, and particularly any “preferred” embodiments,are possible examples of implementations, merely set forth for a clearunderstanding of the principles of the invention. Many other variationsand modifications may be made to the above-described embodiments of theinvention without substantially departing from the spirit and principlesof the invention. All such modifications are intended to be includedherein within the scope of this disclosure and the present invention andprotected by the following claims.

1. An input device for a capacitive touch screen comprising: a rigidtubular shaft having a distal end and a proximal end along alongitudinal axis; an ink cartridge at least partially disposed withinthe tubular shaft movable along the longitudinal axis between a storedposition and an operating position, the ink cartridge having a writingtip that extends beyond the distal end of the tubular shaft at leastwhen in the operating position; and a conductive elastomeric sleevefitted over the distal end of the tubular shaft, the sleeve having afirst end that extends along the longitudinal axis beyond the writingtip of the ink cartridge when the ink cartridge is in the storedposition, a second end extending toward the proximal end of the shaft,and a central hole through which the writing tip extends when the inkcartridge in the operating position; wherein the first end of theconductive elastomeric sleeve is configured to engage and convey inputto the touch screen through physical contact therewith when the inkcartridge is in the stored position.
 2. The input device of claim 1,wherein the sleeve further comprises a hollow rigid inner component forproviding structure to the sleeve and a flexible outer cover forengaging the touch screen and for conducting electricity along thesleeve.
 3. The input device of claim 1, wherein the conductiveelastomeric sleeve provides a textured surface for gripping the inputdevice in hand by a user.
 4. The input device of claim 1, wherein thetubular shaft is formed of a non-conductive material.
 5. The inputdevice of claim 1, wherein the outer diameter of the conductiveelastomeric sleeve begins to decrease beyond a necking point along thelongitudinal axis, and wherein the inner walls of the sleeve form an aircavity beyond the necking point that is substantially wider than thediameter of the writing tip of the ink cartridge.
 6. The input device ofclaim 5, wherein the wall thickness of the conductive elastomeric sleeveis constant along the length of the air cavity.
 7. The input device ofclaim 5, wherein the wall thickness of the conductive elastomeric sleevevaries along the length of the air cavity.
 8. The input device of claim1, wherein the outer diameter of the conductive elastomeric sleevebegins to decrease beyond a necking point along the longitudinal axis,and wherein the wall thickness of the conductive elastomeric sleevevaries such that the central hole through which the writing tip extendshas a substantially constant diameter.
 9. The input device of claim 1,wherein the inner surface of the conductive elastomeric sleeve furtherforms structural ribs along at least a portion of its length, the ribshaving air cavities therebetween.
 10. The input device of claim 1,further comprising a high viscosity coating permanently affixed to atleast a portion of the outer surface of the conductive elastomericsleeve.
 11. A marking device for use with a touch screen comprising: arigid tubular shaft; an ink cartridge at least partially disposed withinthe rigid tubular shaft and movable along the longitudinal axis thereofbetween an operating position and a stored position, the ink cartridgehaving a writing tip at its distal end; and a sleeve connected to adistal end of the shaft, the sleeve comprising: a rigid inner layer thatextends longitudinally beyond the distal end of the shaft; and a pliableouter layer formed of a conductive elastomeric compound that covers andextends longitudinally beyond the rigid inner layer to form a centralhole through which the writing tip extends when the ink cartridge is inthe operating position.
 12. The marking device of claim 11, wherein theportion of the outer layer that extends longitudinally beyond the innerlayer forms an air cavity having a substantially greater diameter thanthe diameter of the writing tip.
 13. The marking device of claim 11,wherein the wall thickness of the portion of the outer layer thatextends longitudinally beyond the inner layer varies such that thecentral hole has a substantially constant diameter along the portion ofthe outer layer that extends longitudinally beyond the inner layer. 14.The input device of claim 11, wherein the inner surface of the outerlayer of the sleeve further forms structural ribs along at least aportion of its length, the ribs having air cavities therebetween. 15.The input device of claim 11, wherein the portion of the inner layerextending longitudinally beyond the tubular shaft forms a springhousing.
 16. The input device of claim 15, further comprising a springdisposed in the spring housing and configured to mechanically assistmovement of the ink cartridge between the stored position and theoperating position.
 17. A marking device kit for use with a touch screencomprising: a rigid tubular shaft; an ink cartridge at least partiallydisposed within the rigid tubular shaft and movable along thelongitudinal axis thereof between an operating position and a storedposition, the ink cartridge having a writing tip at its distal end; andan elastomeric sleeve for connecting to the tubular shaft to form ahousing for the writing tip, wherein the sleeve further comprises: arigid inner component for providing structure to the sleeve; and a firstconductive flexible outer cover for engaging the touch screen when thewriting tip is in the stored position and for conveying electricity fromthe touch screen to a ground; and at least a second conductive flexibleouter cover interchangeable with the first conductive flexible outercover.
 18. The marking device of claim 17, wherein the first conductiveflexible outer cover fits over the rigid inner component of the sleeveto form a first air cavity and wherein the second conductive flexibleouter cover fits over the rigid inner component of the sleeve to form asecond air cavity, wherein the first air cavity has a greater volumethan the second air cavity.